The invention relates to a semiconductor device provided with a semiconductor substrate with a dopant of a first doping type with a doping concentration n1 on which an epitaxial layer with a dopant of a first doping type with a doping concentration n2 is provided, whereon an insulator layer with an opening is deposited, with a Schottky metal layer covering the epitaxial layer lying below said opening, with an annular semiconductor region lying in the epitaxial layer and comprising a dopant of a second doping type with a doping concentration n3 which adjoins the insulating layer and the Schottky metal layer in a region surrounding the metal-insulator transition, and to a method of manufacturing such a semiconductor device.
Schottky diodes are semiconductor devices which have a metal-semiconductor transition as their basic structure and whose basic electronic properties are defined by this transition. A Schottky diode is formed from a semiconductor-metal combination which is chosen such that a depletion zone arises at the boundary surface. The current-voltage characteristic of this arrangement depends on the polarity of the applied voltage.
Although the operating principle of the metal-semiconductor transition in a Schottky diode differs essentially from that of a pn junction, the characteristic curves of a pn diode and a Schottky diode are similar. Compared with a pn diode, a Schottky diode has a lower threshold voltage and a substantially smaller, but strongly temperature-dependent saturation current. In addition, a Schottky diode has a barrier layer capacitance and no diffusion capacitance, which results in shorter switching times. Furthermore, the breakdown characteristic in the blocked state is partly very marked, so that the achievable breakdown voltages are considerably lower than in the case of pn diodes.
To improve and indeed achieve a defined breakdown behavior of a Schottky diode, DE 197 05 728 A1 describes a guard ring of a second doping tape which is diffused into the epitaxial layer of a first doping type. This guard ring achieves that the reverse bias voltage, which is low in the case of a normal Schottky diode, is substantially increased in comparison therewith. This effect is achieved in that the gradient of the field lines of the edge field of the metal electrode, i.e. the Schottky metal layer, is linearized through the fact that it ends at least partly in the ring-shaped semiconductor region of the second doping type.
The properties of a semiconductor device laid down in a specification are determined by the materials used, the design of the semiconductor device, and the doping profiles.
After a semiconductor device has been manufactured, a wide variety of, for example, growing, implantation, and diffusion processes may be carried out. The design of a semiconductor device is defined by a set of masks which depends on the specification. Each additional manufacturing step or masking step, however, is very expensive because it increases the processing time of the wafers in manufacture and leads to a higher personnel and machine expenditure.
The invention has for its object to provide an improved semiconductor device which can be manufactured with simple processes and the lowest possible number of process steps.
This object is achieved by means of a semiconductor device provided with a semiconductor substrate with a dopant of a first doping type with a doping concentration n1 on which an epitaxial layer with a dopant of a first doping type with a doping concentration n2 is provided, whereon an insulator layer with an opening is deposited, with a Schottky metal layer covering the epitaxial layer lying below said opening, with an annular semiconductor region lying in the epitaxial layer and comprising a dopant of a second doping type with a doping concentration n3 which adjoins the insulating layer and the Schottky metal layer in a region surrounding the metal-insulator transition, with a doping region present in the epitaxial layer and comprising a dopant of a first doping type with a doping concentration n4 and the dopant of a second doping type with a doping concentration n3 along the outer contour of the semiconductor device, and with an oxide layer which is present on the epitaxial layer, which adjoins the insulating layer, and which extends along the outer contour of the semiconductor device.
Such a semiconductor device comprises not only a guard ring but also a doping region along the outer contour of the diode. This doping region, also referred to as channel, is advantageous in preventing so-called channel currents. These channel currents flow between the guard ring and the separation lane, when the semiconductor device is biased in reverse direction.
A further advantageous embodiment is formed by the oxide layer along the outer contour of the diode. The outer contour at the same time represents the separation lane which delimits the individual semiconductor devices on the wafer. The oxide layer in the separation lane prevents the crystal from showing excessive fractures at the edge and being damaged during sawing.
It is preferred that the doping concentrations n1 and n4 are higher than the doping concentration n2.
It is furthermore preferred that the doping concentration n4 is higher than the doping concentration n3.
A doping region, the channel, is obtained in the epitaxial layer which prevents a breakdown of the semiconductor device at low voltages already, thanks to the different doping concentrations.
It is preferred that the material for the semiconductor substrate and the epitaxial layer comprises silicon.
Silicon has higher admissible operational temperatures than other semiconductor materials such as, for example, germanium.
It is furthermore preferred that the dopant of the first doping type is chosen from the group comprising P, As, and Sb.
It is furthermore preferred that the dopant of the second doping type is chosen from the group comprising B, Al, and Ga.
The different doping profiles render possible the manufacture of a wide range of semiconductor devices with non-linear current-voltage characteristics.
It is advantageous when the insulating layer and the oxide layer comprise SiO2.
SiO2 has a high chemical resistance, a low thermal conductivity, and a high coefficient of thermal expansion.
It is preferred that the Schottky metal layer comprises a material chosen from the group Al, Mo, W, Pt, Pd, Ag, Au, Ti, Ni, NiFe, and combinations of these materials.
Mo, W, Pt, Pd, Ag, Au, Ni, and Ti are metals with a high work function which do not diffuse into the semiconductor material. Although aluminum is not a metal with a high work function, it does present advantages as a Schottky metal layer at high voltages.
It is preferred that a protective layer is provided on the insulating layer and the oxide layer.
The protective layer protects the subjacent layers against mechanical loads and corrosion by moisture.
It is particularly preferred that the semiconductor device is a Schottky diode.
The semiconductor device is a so-called Schottky hybrid diode, because it has a guard ring.
The invention further relates to a method of manufacturing a semiconductor device provided with a semiconductor substrate with a dopant of a first doping type with a doping concentration n1 on which an epitaxial layer with a dopant of a first doping type with a doping concentration n2 is provided, whereon an insulator layer with an opening is deposited, with a Schottky metal layer covering the epitaxial layer lying below said opening, with an annular semiconductor region lying in the epitaxial layer and comprising a dopant of a second doping type with a doping concentration n3 which adjoins the insulating layer and the Schottky metal layer in a region surrounding the metal-insulator transition, which method comprises at least the steps of:
generating an epitaxial layer with a dopant of a first doping type with a doping concentration n2 on a semiconductor substrate comprising a dopant of a first doping type with a doping concentration n1,
depositing an insulating layer on the epitaxial layer,
exposing an annular region and a region adapted to the outer contour of the semiconductor device in the insulating layer,
implanting a dopant of a second doping type with a doping concentration n3 into the exposed regions of the epitaxial layer,
diffusing the dopant of the second doping type into the epitaxial layer,
depositing an oxide layer on the exposed regions of the epitaxial layer,
implanting a dopant of a first doping type with a doping concentration n4 into the oxide layer,
exposing an opening in the insulating layer,
diffusing the dopant of a first doping type from the oxide layer into the epitaxial layer,
depositing a Schottky metal layer, and
separating along the outer contour of the semiconductor device.
The method has the advantage that no more than eleven process steps with a total of two masks are required for manufacturing this semiconductor device. The manufacturing cost can be kept low as a result of this.
It may be advantageous that a protective layer is deposited on the insulating layer and the oxide layer before the Schottky metal layer is deposited.
The invention will now be explained in more detail below with reference to four Figures and an embodiment, wherein